Perkins is charged with involuntary manslaughter, aggravated assault, obstruction of justice, and lying to investigators.
The judge dropped conspiracy charges against him and Army First Lieutenant Jack Saville, 24, and the men now face up to 26 years in prison if convicted.
The defense denies that Zaidoun Hassoun died in the river near Samarra. Saville's trial was postponed until March after a judge ordered the victim's body to be exhumed for an autopsy and identification.
Soldiers testified Tuesday that they thought the Iraqi pair seemed suspicious and were out past the 11 p.m. curfew. They also said the plumbing equipment they were carrying could be used to make bombs.
Marwan Hassoun testified that he and his cousin were out after curfew because their truck had broken down.
He said Zaidoun Hassoun clung to the soldiers who pushed him before eventually falling into the cold water.
''They had the rifles aimed toward us, but they thought that we were dying," Marwan Hassoun testified. Under questioning by the six-man jury of Army officers, he said the soldiers did not fire their weapons.
Hassoun testified he couldn't touch the bottom of the swift river, but several soldiers testified Tuesday that the water was not deep and there was virtually no current.
Military prosecutors rested their case shortly after Hassoun's testimony. The first defense witness, Staff Sergeant William R. Jackson, testified that he saw two Iraqis climb out of the river.
Perkins and Saville are part of the Third Brigade Combat Team out of Fort Carson, Colo., which is part of the Fourth Infantry Division based at Fort Hood.
In San Diego, meanwhile, a former Navy SEAL testifying under a grant of immunity said he first witnessed prisoner abuse a week after his arrival in Iraq in October 2003.
The sailor, whose identity was not revealed, recalled an incident during which a hooded and handcuffed detainee was kneed, punched, and had his testicles twisted by SEALs in the back of a Humvee.
The sailor served in Iraq under a Navy SEAL lieutenant who faced an Article 32 hearing, the military equivalent of a civilian grand jury, at Naval Base San Diego.
